Sampled Moving Average Notch Filter for Chopper Amplifier Ripple
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Solution Overview
Problem
Chopper-stabilized operational amplifier circuits produce large ripple noise due to offset voltage shifting, and existing notch filters require precise phase alignment with the chopper clock, making them sensitive to clock skew.
Innovation Solution
A chopper-stabilized amplifier design incorporating a sampled moving average notch filter with differential inputs and notch clock signals of varying phases to cancel ripple voltages, allowing for tolerance to clock skew between the chopper and notch filter clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a switched capacitor notch filter is used to reduce ripple noise, then ripple attenuation is improved, but the system becomes sensitive to clock skew between chopper and notch filter clocks
Solution Approach 1:
The notch filter is divided into multiple parallel filter paths (first, second, third notch filters) with different clock phases. Each path processes the same input signal but with different phase relationships to the chopper clock, and their outputs are combined to achieve phase-independent ripple rejection.
Solution Approach 2:
The system dynamically adapts to clock skew by using multiple clock phases (0°, 60°, 120°) that are selectively activated or combined based on the actual phase relationship between the chopper clock and notch filter clock, allowing the filter to maintain effectiveness despite timing variations.
2Object-affected harmful factors
If a switched capacitor notch filter operates at precisely 90 degrees out of phase with the chopper clock, then ripple elimination is maximized, but any phase skew results in residual ripple
Solution Approach 1:
Instead of relying on a single precise 90-degree phase alignment, the invention segments the filtering function across multiple parallel paths with different fixed phase shifts (0°, 60°, 120°). The combination of these paths provides robust ripple rejection without requiring precise phase matching.
Solution Approach 2:
The system changes the phase parameter from a single critical 90-degree value to multiple discrete phase values (0°, 60°, 120°) distributed across parallel filter paths. This parameter diversification makes the system tolerant of phase variations and eliminates the need for precise single-point alignment.
3Object-affected harmful factors
If chopper stabilization is applied to reduce offset voltage and flicker noise, then low-frequency noise performance is improved, but large ripple noise is introduced at the chopping frequency
Solution Approach 1:
The notch filter acts as an intermediary component between the chopper stabilization stage and the output. It selectively attenuates the ripple frequency components generated by chopping while allowing the beneficial offset and flicker noise reduction to pass through, thus mediating between the conflicting effects of chopper stabilization.
Solution Approach 2:
The notch filter extracts and removes the harmful ripple frequency components from the amplifier output signal. By targeting and eliminating only the specific chopping frequency components, it separates the harmful ripple from the useful signal that has benefited from chopper stabilization.
Data Source
AI summary
A chopper-stabilized amplifier includes a first transconductance amplifier and a first chopper circuit coupled to an input of the first transconductance amplifier. A second chopper circuit is coupled to an output of the first transconductance amplifier. The chopper-stabilized amplifier also includes second and third transconductance amplifiers having inputs coupled to the output of the first transconductance amplifier. The second transconductance amplifier produces an output responsive to a first notch clock signal having a first phase relative to the chopping of the second chopper circuit. The third transconductance amplifier produces an output responsive to a second notch clock signal having a second phase relative to the first phase. The output signals produced by the second and third transconductance amplifiers are added to filter ripple noise at the outputs of the second and third transconductance amplifiers.